Tabbed browsing has been one of the key recent improvements to the web. It's made it far easier to work with multiple pages - many people keep dozens of tabs open for days, waiting for the opportunity to read or complete them. It was one of the main selling points behind Internet Explorer 7.
And yet, tabbed browsing is terrible. You can't resize, reshape and move tabs, like you can normal windows - they're all stuck at the size of the browser window. You can't search across every tab. And they blatantly overlap with the taskbar, for those using Windows.
Is there a better approach than tabs? Sure - think how you organise pieces of paper on a desk. They're in piles, at various angles, and at any point you can bring them to the front and work on them. But hmm - pieces of paper tend to get lost or crumpled under others.
I still don't think anyone has properly implemented a simple, powerful, and intuitive interface for working with multiple documents visually. That seems ridiculous - what on earth have we been doing for so long!
We can guess at what a solution might look like - a multi-touch screen allowing document resize and zoom, a quick search function across open documents, some way to remember default document dimensions. Some combination of Mozilla SVG photos and Jeff Han's multi-touch.
In the meantime it's worth pointing out that, for all their advantages, tabbed browsers are only a quick and dirty fix to the problem of working across multiple documents.